1. Field of the Invention
This invention is generally directed to rendering an operation condition of a photoresist coating system. More specifically, the present invention relates to a photoresist coating system that efficiently limits any damage caused by any bubble in photoresist.
2. Description of the Prior Art
Because most available photoresists are liquid, it is necessary to pump photoresist from a reservoir to a reactor where photoresist is dispensed and coated on a wafer. Moreover, in most present photoresist coating systems, not only are both pump and pipeline desired, but also a tank is inserted into the pipeline to adjust a flow rate of photoresist before the photoresist is pumped into the pump and sent to the reactor. In other words, the photoresist coating system is designed to let the photoresist be continually and uniformly dispensed on the wafer.
Of course, owing to the fact that in many contemporary semiconductor processes several kinds of photoresists are required, most available photoresist coating systems comprise several pumps, several reservoirs and several tanks, and only one reactor. However, only one reservoir, one pump, one tank and one pipeline are desired for each kind of photoresist.
It is well known that the forming process of the photoresist layer is affected by existence of bubbles in photoresist. When any bubble is pumped into the pump, it also is sent into the reactor, therefore, the quantity of photoresist that is dispensed on the wafer is fluctuant and the distribution of photoresist on the wafer also is not uniform, and then the quality of photoresist layer is degraded by the bubble. In addition, the source of bubbles comprises the incomplete sealing of pipelines of the photoresist coating system and improper operation of the pump of the photoresist coating system.
To avoid possible disadvantages of the existence of the bubble, conventional photoresist coating systems broadly use a capacitor sensor to detect the existence of the bubble. A capacitor sensor is attached to the tank, and particularly is attached on the sidewall of the tank, and the existence of a bubble will change the capacitance and will be detected.
However, the detecting ability of the capacitor sensor is limited by several factors. First, the sensitiveness of the capacitor sensor is dependent on the density of photoresist. The lower the density is, the worse the sensitivity. Second, manual adjustment is necessary to adjust the critical point of response of the capacitor sensor. In other words, when a different photoresist is used, the capacitor sensor must be adjusted and it is difficult to properly adjust it. Besides, when photoresist with low density is used, the exactness of the capacitor sensor is bad.
Additionally, in most of conventional photoresist coating systems, the tank is not adjacent to the pump, thus, any bubble formed inside a section of pipeline between the tank and the pump could not be detected by the capacitor sensor.
Therefore, according to the previous discussion, it is crystal-clear that capacitor sensor cannot provide enough protection to prevent any bubbles pumped into pump and reactor, and it is necessary to develop a new photoresist coating system to provide the required protection.
A primary object of the invention is to prevent the quality of photoresist coating system from being degraded by bubbles in photoresist.
An additional object of the invention is to improve the quality of photoresist layer that formed on a wafer.
A further object of the invention is to propose a photoresist coating system that is suitable for many kinds of photoresist.
The related embodiment of the present invention is a photoresist coating system for coating a photoresist layer where material of photoresist is liquid. The present embodiment comprises: a pump for pumping photoresist from a reservior into photoresist coating system, a tank for maintaining a flowing rate of photoresist in an approximately fixed value before it is pumped into the pump, a reactor where photoresist is dispensed and coated on a wafer to form photoresist layer, a first pipeline for conveying photoresist from reservoir to tank, a second pipeline for conveying the photoresist from the tank to the pump, and a third pipeline for conveying the photoresist from the pump to the reactor.
Moreover, the embodiment further comprises a capacitor sensor that is coupled to the tank, a photochopper sensor that is coupled to the second pipeline and a controller that is coupled to both capacitor sensor and photochopper sensor. Therefore, any bubble inside the tank is detected by the capacitor sensor and any bubble inside the second pipeline is detected by the photochopper sensor. When a warning message from these sensors is received by the controller, the controller will alarm and terminate the operation of the photoresist coating system.
In short, the key points of the invention comprise both capacitor sensor and photochopper sensor used to detect the existence of a bubble in the photoresist, and a controller is used to alarm and terminate operation of the system when a bubble is detected by at least one sensor.